A system for invitro inhaled/exhaled aerosol testing of personal protective equipment

Social distancing at six feet (about two meters), frequent hand hygiene, and using personal protective equipment (PPE) such as masks and shields are common practices to reduce the transmission of airborne viruses. An in-vitro system for testing and comparing a selection of PPE to prevent aerosol escape and aerosol intrusion at three distances and three angles is described. In the system tested, at six feet, face masks or shields provided markedly decreased aerosol transmission in a room with limited ventilation. At two feet, with a type of protection wearing manikin emitting aerosols of normal saline and a non-barrier receiver, the aerosol transmission increased with the use of a KN95 (+ 20%), a washable cloth mask (+ 25%), a disposable shield (+ 7%), a 3D printed shield (+ 3%), and a shop shield (+ 15%) compared to the case with no PPE used on either. Changing the angle at which the two manikins are facing each other affected aerosol transmission; compared to the manikins wearing an N95 mask and facing each other, an angle of 45° and 90° increased transmission by 43% and 52%, respectively. With both the generator and receiver wearing a disposable medical mask, aerosols detected at all distances were significantly attenuated. In the system tested, masks generally provided superior aerosol transmission reduction when compared to face shields. These resultsare not intended to guide PPE selection but may serve as a framework for future research and advanced testing methodology. It is reassuring to confirm however that the distance between the aerosol transmitter and receiver significantly reduced aerosol exposure and that a simple surgical mask worn by both transmitter and receiver markedly reduced transmission to near background levels. The manikin represents a scaled-down model; therefore, absolute flow fields differ from adult physiology. The findings should be interpreted in relative rather than absolute terms.